For close to eight months now -- since she released the music video for her song “We Can’t Stop” -- Miley Cyrus has had a look in her eyes that’s proved nearly as transfixing as the other body parts she’s put on public view.

It’s a mixture of determination and desperation, a raw visual expression of how brazenly the former Disney Channel star has remade herself in a hip-hop image but also, it seems, of a creeping fear that her license to appropriate may be revoked at any moment.

Given the degree to which it was promoted in advance as a kind of “hoedown throwdown” (to borrow the title of one of her old Hannah Montana songs), you might’ve expected the anxiety to dissipate for Cyrus’ edition of MTV’s “Unplugged,” which premiered Wednesday.

“I don’t know if you guys know this or not, but I’m from Nashville,” she told the studio audience shortly after vaulting onstage in a tight red-gingham jumpsuit. “And since I couldn’t make all of you guys go back home with me, I tried to bring Nashville here for tonight.”

Yet if the 21-year-old singer was returning to the safety of her roots, that fear of being found out still flickered across her eyes, even when they were obscured beneath a blond wig evidently intended as an homage to Dolly Parton. For Cyrus, described in a commercial near the end of the hour-long broadcast as “the most talked-about artist on the planet,” the work of reinvention never ends.

That restlessness made for intermittent thrills on “Unplugged,” for which she and a band playing mostly acoustic instruments performed on a stage set to resemble a barnyard, with a giant light-up wagon wheel overhead. (Time will tell whether the arrangements from this show figure into the North American arena tour Cyrus is to launch next month.)

In “4X4” and “#GETITRIGHT,” a pair of already-twangy funk cuts from last year’s “Bangerz” album, her nervous energy gave the music a jittery quality rarely voiced in the ultra-polished pop that dominates Top 40 radio.

“I’ve been laying in this bed all night long / Don’t you think it’s time to get it on?” she sang in “#GETITRIGHT” -- an appealingly petulant come-on from someone caressing a guy in a horse costume, as Cyrus was.

“Rooting for My Baby” had a similar friction, with the neediness in her voice playing against the dreamy thrum of a song channeling “Rumours”-era Fleetwood Mac. And though she’s likely sung it dozens (if not hundreds) of times over the last year, Cyrus seemed to access a fresh reserve of hurt for “Wrecking Ball”; she rushed the ballad in a way that suggested she hasn’t grown inured to its power.

At other points, though, Cyrus’ reaching felt more like grasping, as in a frantic, tuneless “SMS (Bangerz)” and “Drive,” a dreary piano ballad in which her intensity seemed to lack a specific target. Ditto her cover of Parton’s “Jolene,” which she sang well enough but didn’t endow with any meaning deeper than her respect for country-music show business.

Not that show business can’t provide its own meaning. For Wednesday’s much-hyped closer, Cyrus brought Madonna onstage for an ungainly mash-up of “We Can’t Stop” and Madonna’s “Don’t Tell Me,” two declarations of pop-star intransigence from women who’ve faced plenty of opposition.

And though the song sounded terrible, there was something undeniably exciting about watching the singers continue to say no -- Madonna to those who insist she give it up, Cyrus to those who demand she just be herself.